AN426 instead of AN470... structural issue?

[HighSchoolBuilders]

Hi All,

I made a mistake of countersinking a component that calls for AN470 (namely FL-706B to FL-704 on the flap assembly). The countersunk part is 0.125" thick so it's well within limit of thickness for countersinking. However, the shop head will now has to be formed on the thinner material (0.025") of the FL-704 end rib.

1) Will I be jeopardizing the structural integrity of the assembly if I went from AN470 to a AN426?

2) If not, will it be a problem if I form the shop head on the thinner material?

3) if yes, will fabricating a reinforcement plate with a 0.030" or thicker material help, to allow the shop head form on the thicker material instead of straight on the thinner rib skin? (Sandwich the 0.025" material with 0.125" and 0.030", with shop head on the 0.030" material)?

Many many thanks for your input! The manual says "the flaps are the easiest control surfaces on the RV8/8A to build"....and I managed to screw this one up.

Cheers!
Hank

[GAHco]

Originally Posted by HighSchoolBuilders

Hi All,

I made a mistake of countersinking a component that calls for AN470 (namely FL-706B to FL-704 on the flap assembly). The countersunk part is 0.125" thick so it's well within limit of thickness for countersinking. However, the shop head will now has to be formed on the thinner material (0.025") of the FL-704 end rib.

1) Will I be jeopardizing the structural integrity of the assembly if I went from AN470 to a AN426?

2) If not, will it be a problem if I form the shop head on the thinner material?

3) if yes, will fabricating a reinforcement plate with a 0.030" or thicker material help, to allow the shop head form on the thicker material instead of straight on the thinner rib skin? (Sandwich the 0.025" material with 0.125" and 0.030", with shop head on the 0.030" material)?

Many many thanks for your input! The manual says "the flaps are the easiest control surfaces on the RV8/8A to build"....and I managed to screw this one up.

Cheers!
Hank

You may be able to dimple the thin skin, countersink the thick piece to accept the dimple, and finally form the shop head on the non countersunk side. This should maintain an equivalent strength for your structure.

Best wishes.

[HighSchoolBuilders]

Unfortunately, the piece i countersunk is unidirectional, I already countersunk the "outside", which left me no choice...

[RV6AussieNick]

you can install a uni head rivet on the thin side and form the tail in the countersink. Rule of thumb is head on the thin side, tail on the thick side, if you try to form the tail on the thin side the material will pucker up around the tail.

[HighSchoolBuilders]

What if I put a thick piece of material on top of the thin material? Will that be okay?

[az_gila]

The shear strength of the two rivets will be identical.

Try it and if the thin skin side doesn't wrinkle/pucker you are good to go. If you have a good 1.5D x 0.5D shop head you will have no loss of strength.

If it does wrinkle, remove the rivet and try a doubler...

[bret]

Look at how you do the rudder T.E. ?

[HighSchoolBuilders]

Thanks guys for all the quick response!

No wrinkle in my case, good to go

Thanks!
Hank